1. Technical Field
The present invention relates to a linear modulation voltage transformer circuitry and, more particularly, to a linear modulation voltage transformer configured for real-time voltage transformation.
2. Description of Related Art
Voltage transformers serve to convert an input power, such as an input current, into an output power of a certain specification, such as a specific output voltage. For example, a common analog voltage transformer typically uses two voltage divider resistors to step down an input voltage to a specific or a predetermined voltage.
Please refer to FIG. 1 for the circuitry of a conventional voltage transformer and to FIG. 2 for a block diagram of the conventional voltage transformer.
As shown in FIG. 1, the circuitry of a conventional voltage transformer 10 includes a power stage unit 30, a voltage division unit 40, an error amplifier 50, and a recursive controller 60, wherein the output end of the recursive controller 60 connects to the power stage unit 30.
The power stage unit 30 is configured for step-up, step-down, and step-up/down voltage conversion so as to convert an input voltage 20 into an output voltage of a certain specification.
The voltage division unit 40 is connected to the power stage unit 30 and includes two voltage divider resistors. The voltage division unit 40 can use different voltage divider resistors to divide the input voltage 20 at different ratios according to the voltage specification of a load circuit and then outputs a divided voltage VR to the error amplifier 50.
The error amplifier 50, which includes a first impedance 51, a second impedance 52, and an amplifier 53, receives the divided voltage VR, compares the divided voltage VR with a reference voltage VRef, amplifies the voltage difference therebetween, and outputs an error gain control signal EGS to the recursive controller 60. The error gain control signal EGS serves as a basis on which the power stage unit 30 determines whether to perform step-up, step-down, or step-up/down voltage conversion.
The recursive controller 60 is a pulse width modulator 61 for modulating the pulse width of the error gain control signal EGS, generating a gain control signal GCS suitable for the power stage circuit, and outputting the gain control signal GCS to the power stage unit 30. Therein, a check voltage VMag is a necessary parameter for pulse width modulation of the error gain control signal EGS.
As shown in FIG. 2, the power stage unit 30, the voltage division unit 40, the error amplifier 50, and the recursive controller 60 form a closed-loop circuit that provides stable and continuous feedback so as to output a voltage meeting the load demand of a specific load circuit.
Presently, the conventional voltage transformer 10 is applicable only to load circuits of a certain voltage specification. If it is desired to apply the voltage transformer 10 to load circuits of different voltage specifications, the output voltage of the voltage transformer 10 must be varied.
One common solution to varying the output voltage of the conventional voltage transformer 10 is to use a variable resistor as the voltage division unit 40. However, the disadvantage of using the variable resistor is that the resistance must be manually adjusted, which may result in over-adjustment and subsequent damage to the circuit, and that real-time adjustment is unattainable.
Another common solution is to change the reference voltage VRef and thereby change the error gain control signal EGS output from the error amplifier 50. Since the reference voltage VRef of an analog circuit is built-in to the circuit in advance and therefore unchangeable, this solution is applicable only to a digital voltage transformer. However, once the circuit is burned into an IC, all the divided voltages are fixed; hence, it is impossible to change the output voltage by varying the reference voltage VRef.